Electric incandescent lamp comprising an internal fuse

ABSTRACT

A halogen filament lamp comprising an internal fuse having at least two conductors of different diameters electrically connecting series arranged filaments to current conductors embedded within the pinch seal.

United States Patent [191 Notelteirs et all,

Feb. 20, 1913 ELECTRIC INCANDESCENT LAMP COMPRISING AN INTERNAL FUSE Inventors: Victor Rosalie Notelteirs; Eduard Jozef Philomena Janssen, both of Emmasingel, Eindhoven, Netherlands Assignee: U.S. Philips Corporation, New

York, N.Y.

Filed: Feb. 19, 1970 Appl. No.: 12,692

Foreign Application Priority Data Feb. 21, 1969 Netherlands ..6902806 US. Cl ..313/217 Int. Cl. ..H01j 17/04 Field of Search ..313/222, 315, 333, 443, 315,

[56] References Cited UNITED STATES PATENTS 3,496,403 2/1970 Palermo et al ...313/279 X 3,423,622 1/1969 Rowe ...313/331 X 3,441,772 4/1969 Cardwell, Jr. ..313/222 X 2,864,025 12/1958 Foote et a1 ..313/315 X Primary Examiner-Nathan Kaufman Attorney--Frank R. Trifari [57] ABSTRACT A halogen filament lamp comprising an internal fuse having at least two conductors of different diameters electrically connecting series arranged filaments to current conductors embedded within the pinch seal. 1

3 Claims, 4 Drawing Figures PATENTED FEB 2 0 i973 SHEET 2 OF 2 fig.4

Jury 7' ELECTRIC INCANDESCENT LAMP COMPRISING AN INTERNAL FUSE The invention relates to an electric filament lamp, particularly a mono-pinch halogen filament lamp, which comprises a tubular lamp vessel in which metal foils having secured thereto current beams projecting from the lamp are sealed in a pinch seal to which foils a preferably coiled-coil filament which may consist of a few series-arranged parts is electrically connected. Such a filament lamp is known as a mono-pinch halogen filament lamp for copying purposes. In such a lamp, a filament which is composed of a few series-arranged parts is incorporated with its two ends in the pinched seal and is secured to the foils which are sealed in said pinch seal.

It is the object of the invention to provide a monopinch filament lamp which has an internal fuse in such manner that in the switched-on condition it does not explode at the end of the life of the lamp. (When the switched-on lamp fuses, nearly always a discharge lamp is formed in which an arc is maintained which in the case of sufficient duration can cause the lamp seal and even the lamp housing connections to fuse and give rise to lamp explosions). It has been found that this is very hard to realize, particularly in mono-pinch halogen lamps since in these lamps the foils with the wire parts projecting in said lamp space are situated at a very short distance from one another. It is then desirable to have the disposal of an extremely rapidly reacting fuse.

During the investigation of this type of filament lamp to be provided with an internal fuse, it has surprisingly been found that an extremely rapidly operating internal fuse is obtained when the filament in said lamp is secured, at least at its one end in a place situated inside the lamp vessel, to the ends of at least two conductors of different diameters projecting from the adjacent pinch seal in said space, which conductors are themselves connected in said pinch seal to the foil present therein.

It is to be noted that it is known per se to form fuses from a number of parallel-arranged wires of mutually different materials in which wires of different melting characteristics are obtained.

However, said fuse is on the one hand unfit for incorporation in an electric filament lamp for example, a halogen filament lamp, in which the choice of the materials to be used is restricted. In the known fuses materials are'used which melt at a considerably lower temperature than that which occurs in forming monopinch seals at the end of the tube of, for example, quartz glass. On the other hand the known fuses do not use current conductors of mutually different diameters.

According to a first embodiment of the electric filament lamp according to the invention which comprises one pinch seals, the two conductors are formed as wires extending parallel between the filament and the foil.

According to a second embodiment of the lamp according to the invention which comprises only one pinch seal, the conductor having the smaller diameter is wound helically around the other conductor, and the resulting mandrel is screwed in the filament over part of its length. This embodiment has the additional advantage that this combination of conductors formed as a mandrel can particularly simply be screwed in one end of the filament so that a rigid connection with the filament is obtained.

It will be obvious that the invention can advantageously be used in many types of halogen filament lamps which comprise a rather compact light source and in which an identical assembly of conductors serving as an internal fuse is present at either end of the filament.

In order that the invention may be readily carried into effect, two embodiments thereof will now be described in greater detail, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a longitudinal cross-sectional view of a first embodiment of a mono-pinch halogen lamp for copying purposes,

FIG. 2 shows on an enlarged scale the connection of the filament to the foil incorporated in the pinch seal of the lamp shown in FIG. 1,

FIG. 3 is a cross-sectional view analogous to that shown in FIG. 1 ofa lamp to a second embodiment,

FIG. 4 is an enlarged cross-sectional view analogous to that shown in FIG. 2 of the connection of the filament to the foil incorporated in the pinch seal of the lamp shown in FIG. 3.

The I000 Watt halogen lamp shown in FIG. 1 which is operated at 225 Volts comprises a tubular lamp vessel l which is closed at one end by a flat pinch 3 and at the other end is closed by its sealed exhaust tube 5. The lamp vessel is filled with a halogen-containing gas filling which will not be further described.

A filament composed of two series-arranged parts 7 and 9 is stretched in the lamp. In the ends of this filament which is arranged entirely in the lamp space 11, mandrels 13 and 15 are screwed which themselves are incorporated in a quartz glass beam 19 together with a supporting wire 17. The supporting wire 17 is incorporated in the pinch seal 3 and comprises at its free end a location in which the part 8 between the filaments 7 and 9 is supported. The mandrels l3 and 15 are each formed from a set of conductors 21, 23 and 25, 27, respectively. They are connected to the molybdenum foils 29 and 31. The projecting beams 33 and 35 are secured to the foils 29 and 31 in any conventional manner.

It has been found that in the lamp construction shown the conductors formed as wires 21, 23 and 25, 27, respectively, can serve as internal lamp fuses which prevent the switched-on lamp from exploding at the end of its life. In the embodiment shown the two wires 21, 23 and 25, 27, respectively, are of tungsten and have different diameters. The wire 21 has a diameter of 150 p. whereas the wire 23 has a diameter of 100 a. Satisfactory fuse results have been found-possible when one wire is between 20 and percent thicker than the other wire.

It is shown in detail in FIG. 2 how the two wires 21, 23 are secured to the filament. The end of the filament 7 is denoted by four turns 37. In this end, a mandrel is incorporated which is formed as a central rod 39 of tungsten having a wire 41, likewise of tungsten, helically wound thereon. The resulting mandrel is directly screwed with its one end in the end of the filament 7 and may be provided with an auxiliary coil 43. The assembly is incorporated in the above-mentioned quartz beam 19 which actually consists of two halves 45 and 47 which, after having been heated to melting, are forced together with the interposition of the end of the filament 7 having screwed therein the end of the mandrel 39, 41 described, and constitute a beam 19 after cooking. In an analogous manner the supporting wire 17 and the end of the other filament 9 are incorporated in the beam 19. By means of the supporting wire 17, the beam 19 is hence spaced apart from the pinch seal 3. The wire 21 provided with a few helically extending turns 49 is now screwed around the mandril while the wire 23 provided with analogous turns 51, is screwed around another part of the mandrel.

'Ihe halogen filament lamp according to the embodiment shown in FIG. 3 is constructed in an analogous manner as the copying lamp shown in FIG 1. In this lamp also the two ends of the filaments 55 and 57 are incorporated in a quartz beam 53 and the foils 59 and 61 are connected to the ends of the filaments 55 and 57 by means of two wires 63, 65 and 67, 69. In contrast with the lamp shown in FIG. 1, said wires do not extend parallel to each other, but are formed as mandrels in which the conductor (63) having the smaller diameter (again 100 p.) is wound helically around the thicker conductor (150 u) constructed as a straight wire 65 (see FIG. 4). The mandrel shown is again screwed in the end of the filament 55, if desirable with the interposition of an auxiliary coil 71.

What is claimed is:

1. An electric filament lamp comprising an evacuated tubular envelope having a pinch seal at one end, a

halogen atmosphere within said envelope, a first pair of current conductors embedded within said pinch seal, two series arranged filaments stretched parallel to each other in a longitudinal direction within said envelope, and a supporting wire within said envelope and embedded in said pinch seal for supporting said filaments, each of said filaments being electrically coupled within said envelope to one of said first pair of current conductors through a second pair of parallel-connected conductors proximate to each pinch seal, one of said second pair of conductors having a cross-sectional area greater than the other of said second pair thereby providing a rapid acting internal fuse for said lamp, which fuse acts to prevent high current arcs from occurring at the end of lamp life and consequently prevents lamp explosion.

2. An electric filament lamp as claimed in claim 1 wherein said two connected conductors of different cross sectional areas are formed of wires extending in parallel between the filament and said pinch seal.

3. An electric filament lamp as claimed in claim 1 wherein said conductor having the smaller cross-sectional area is wound helically around the conductor having the greater cross-sectional area to form a mandrel that is screwed into said filaments over a part of its length. 

1. An electric filament lamp comprising an evacuated tubular envelope having a pinch seal at one end, a halogen atmosphere within said envelope, a first pair of current conductors embedded within said pinch seal, two series arranged filaments stretched parallel to each other in a longitudinal direction within said envelope, and a supporting wire within said envelope and embedded in said pinch seal for supporting said filaments, each of said filaments being electrically coupled within said envelope to one of said first pair of current conductors through a second pair of parallel-connected conductors proximate to each pinch seal, one of said second pair of conductors having a cross-sectional area greater than the other of said second pair thereby providing a rapid acting internal fuse for said lamp, which fuse acts to prevent high current arcs from occurring at the end of lamp life and consequently prevents lamp explosion.
 1. An electric filament lamp comprising an evacuated tubular envelope having a pinch seal at one end, a halogen atmosphere within said envelope, a first pair of current conductors embedded within said pinch seal, two series arranged filaments stretched parallel to each other in a longitudinal direction within said envelope, and a supporting wire within said envelope and embedded in said pinch seal for supporting said filaments, each of said filaments being electrically coupled within said envelope to one of said first pair of current conductors through a second pair of parallel-connected conductors proximate to each pinch seal, one of said second pair of conductors having a cross-sectional area greater than the other of said second pair thereby providing a rapid acting internal fuse for said lamp, which fuse acts to prevent high current arcs from occurring at the end of lamp life and consequently prevents lamp explosion.
 2. An electric filament lamp as claimed in claim 1 wherein said two connected conductors of different cross sectional areas are formed of wires extending in parallel between the filament and said pinch seal. 